Rotation angle detector

ABSTRACT

The present invention relates to a rotation angle detector for use mainly in detecting rotation angles of a vehicle&#39;s steering shaft with a simplified and low-cost configuration. For the purpose, the first detection head and the second detection head are disposed perpendicularly to the rotor, and the spur gear formed outside the periphery of the first detection head is allowed to engage with the gear formed on the bottom of the periphery of the rotor. This can provide the first detection head with a simplified configuration and can form magnetic sensors together with a controller on a single circuit board. The configuration enables the rotation angle detector to perform the detection reliably and cheaply.

FIELD OF THE INVENTION

The present invention relates to a rotation angle detector for usemainly in detecting rotation angle of vehicle steering shaft.

BACKGROUND OF THE INVENTION

Along with recent advance in vehicle technologies, a variety of rotationangle detectors for detecting rotation angle of a steering shaft haveincreased to perform various controls in vehicle operation.

A conventional rotation angle detector of the kind is described withreference to FIG. 3. FIG. 3 shows an exploded perspective view of aconventional rotation angle detector. Rotor 1 with spur gear 1A formedoutside the periphery has key 1B provided at the center of inside theperiphery to engage with a steering shaft (not shown) that is insertedthrough rotor 1 as shown in the drawing.

First detection head 2 has spur gear 2A formed outside the periphery andsecond detection head 3 has spur gear 3A formed outside the peripherywith number of teeth different from spur gear 2A. Spur gear 2A of firstdetection head 2 engages with spur gear 1A of rotor 1 and, at the sametime, spur gear 3A of second detection head 3 engages with spur gear 2Aof first detection head 2.

A plurality of wiring patterns (not shown) are formed on the top andbottom surfaces of circuit board 4 disposed below and approximatelyparallel to first detection head 2 and second detection head 3.Meanwhile, magnetic sensors 5B and 6B are mounted on the surface ofcircuit board 4 facing magnet 5A and 6A mounted in the center of firstdetection head 2 and second detection head 3 respectively.

Magnet 5A and magnetic sensor 5B thus facing each other are to form thefirst detection section, and similarly magnet 6A and magnetic sensor 6Bare to form the second detection section respectively.

Circuit board 7 disposed perpendicularly to circuit board 4 andconnected to via lead wires or the like (not shown) includes electroniccomponents such as microcomputers, thereby forming controller 8connected to magnetic sensors 5B and 6B.

Cover 10 made of insulation resin covers the top surface of case 9 madeof insulation resin that includes rotor 1, first detection section 2,second detection section 3 and circuit board 4 or the like; and cover 11similarly made of insulation resin covers a side surface of case 9 thatincludes circuit board 7 and controller 8 or the like, thus completingthe rotation angle detector.

The rotation angle detector with the above configuration is mounted on avehicle, connecting controller 8 to an electronic circuit (not shown) ofthe vehicle via a connector (not shown) or the like, and inserting asteering shaft through the center of rotor 1. Since the steering shaftengages with key 1B, rotor 1 rotates in response to a rotation of thesteering shaft.

In the above configuration, upon rotating the steering shaft whendriving a vehicle, rotor 1 starts rotating, then first detection head 2starts rotating in response to rotor 1, and second detection head 3starts rotating in response to first detection head 2 sequentially.Magnets 5A and 6A mounted in the center of the first and seconddetection heads rotate as well, and accordingly magnetic sensors 5B and6B detect changing magnetic force from magnets 5A and 6A as detectionsignals in voltage waveform including sine waves and cosine waves.

The detection signals are input into controller 8 in a waveform ofsaw-tooth wave. Since first detection head 2 and second detection head 3differ in number of teeth or rotation speed, the waveform from firstdetection head 2 and second detection head 3 differ in frequency cycles,forming phase-shifted detection signals.

Using these two different detection signals from first detection head 2and second detection head 3 together with respective number of teeth,controller 8 runs a predetermined calculation to detect a rotation angleof rotor 1 or the steering shaft, which is then output into theelectronic circuit of the vehicle for use in various controls in vehicleoperation.

Other than the configuration like described above in which spur gearsformed outside the peripheries engage with each other, some models havetried to dispose first detection head 2 and second detection head 3perpendicularly to rotor 1 and to mount magnetic sensors 5B and 6B on asingle circuit board 7, by using bevel gears for rotor 1 and firstdetection head 2 engaged with the rotor 1, thus removing circuit board 4to realize a low-cost configuration.

In this case, however, first detection head 2 needs to be provided withboth a bevel gear to engage with rotor 1 and a spur gear to engage withsecond detection head 3, which causes not only a complicated componentrybut also increase in gear engaging points that tends to cause errorseasily owing to the clearance between respective gears or so-calledbacklash.

Japanese Patent Laid-Open Application No. 2005-156163 is known forinstance as a relevant Information Disclosure Statement (IDS).

However, there has been problems in the above conventional art that therotation angle detector has become expensive owing to the use of twocircuit boards 4 and 7, and has had design limitations in dimensionswhen the diameter of first detection head 2 and second detection head 3are needed to enlarge to increase the number of teeth so as to improvethe detection accuracy of the rotation angle.

SUMMARY OF THE INVENTION

To solve the aforementioned problems, the present invention aims atproviding a rotation angle detector capable of detecting the rotationangle reliably with a simplified and low-cost configuration.

Therefore, the rotation angle detector of the present invention has thefollowing configuration that the first and second detection heads aredisposed perpendicularly to the rotor, and the spur gear formed on theside periphery of the first detection head is allowed to engage with thegear formed on the bottom of the periphery of the rotor. This canprovide the first detection head with a simplified configuration and, atthe same time, can form both magnetic sensors and a controller on asingle circuit board. The configuration enables the rotation angledetector to detect rotation angles reliably and cheaply.

Moreover, a biasing spring provided allows the rotor to contact on thefirst detection head resiliently, which eliminates the clearance betweengears of rotor and the first detection head so-called backlash, enablingthe rotation angle detector to perform highly accurate detection withoutany error.

As described above, the present invention can realize the rotation angledetector capable of detecting reliably with a simplified and low-costconfiguration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exploded perspective view of the rotation angle detectorused in an exemplary embodiment of the present invention.

FIG. 2 shows a partial perspective view of the rotation angle detectorused in another exemplary embodiment of the present invention.

FIG. 3 shows an exploded perspective view of a conventional rotationangle detector.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The exemplary embodiments of the present invention are described nowwith reference to FIGS. 1 and 2. The similar elements described in thebackground art have the same reference marks and details are describedsimply.

Exemplary Embodiments

FIG. 1 shows an exploded perspective view of the rotation angle detectorused in the exemplary embodiment of the present invention. Rotor 21 madeof insulation resin or metal has gear 21A formed on the bottom of theperiphery and has key 21B formed at the center of inside the peripheryto engage with the steering shaft (not shown) that is inserted throughrotor 21 as shown in the drawing.

First detection head 22 made of insulation resin or metal and seconddetection head 23 similarly made of insulation resin or metal aredisposed perpendicularly to rotor 21. Spur gear 22A formed outside theperiphery of first detection head 22 engages with gear 21A formed on thebottom of the periphery of rotor 21. Spur gear 23A formed outside theperiphery of second detection head 23 with number of teeth differentfrom spur gear 22A engages with spur gear 22A of first detection head22.

A plurality of wiring patterns (not shown) are formed on the top andbottom surfaces of circuit board 24 disposed collaterally andapproximately parallel to first detection head 22 and second detectionhead 23. Magnetic sensors 5B and 6B such as anisotropicmagneto-resistive (AMR) elements or the like are fixed by insert moldingor the like on a surface facing magnets 5A and 6A fixed in the center offirst detection head 22 and second detection head 23 respectively.

Magnet 5A and magnetic sensor 5B both facing each other form the firstdetection section and similarly magnet 6A and magnetic sensor 6B formthe second detection section respectively. Controller 8 is formed oncircuit board 24, which includes electronic components such asmicro-computers and is connected to magnetic sensors 5B and 6B.

Rotor 21 is disposed rotatably in hollow cylinder 25A formed on the topsurface of insulation resin-made case 25. First detection head 22 andsecond detection head 23 are disposed rotatably in cylinders 25B and 25Cformed on a side surface of case 25 respectively.

Insulation resin-made cover 26 covers the top surface of case 25 thathouses rotor 21 and similarly insulation resin-made cover 27 covers theside surface of case 25 that houses first detection head 22, seconddetection 23, circuit board 24 or the like.

Spring 28 made of copper alloy, steel plate or the like is disposedbetween the bottom surface of cover 26 and the top surface of rotor 21in a slightly sagged condition to form a biasing spring, causing rotor21 to contact first detection head 22 resiliently thereby completing therotation angle detector.

Namely, disposing first detection head 22 and second detection head 23perpendicularly to rotor 21, spur gear 22A formed on the side peripheryof first detection head 22 is allowed to engage with gear 21A formed onthe bottom of the periphery of rotor 21. Additionally, the same spurgear 22A is allowed to engage with spur gear 23A formed on the sideperiphery of second detection head 23, where first detection head 22 cando with only one gear, thus realizing a simplified configurationconsequently.

Furthermore, magnetic sensors 5B and 6B, controller 8 or the like areall formed on circuit board 24 disposed in the side of first detectionhead 22 and second detection head 23, which can reduce the quantity ofcircuit board to use to only one thereby realizing a low-costconfiguration.

The rotation angle detector with the above configuration is mounted on avehicle, connecting controller 8 to an electronic circuit (not shown) ofthe vehicle via a connector (not shown) or the like, and inserting asteering shaft through the center of rotor 21. Since the steering shaftengages with key 21B, rotor 21 rotates in response to a rotation of thesteering shaft.

In the above configuration, rotating the steering shaft while driving avehicle, or while the rotation angle detector is in an energizedcondition, rotor 21 engaged with the steering shaft rotates in responseto the rotation of the steering shaft and subsequently first detectionhead 22 whose spur gear 22A engages with gear 21A formed on the bottomof the periphery of rotor 21 starts rotating in response to the rotationof rotor 21. Then, second detection head 23 whose gear 23 A engages withspur gear 22A starts rotating in response to the rotation of firstdetection head 22.

Along with rotating of respective detection heads, magnets 5A and 6Amounted in the center of the heads rotate as well and subsequentlymagnetic sensors 5B and 6B detect the changing magnetic intensity frommagnets 5A and 6A as detection signals in voltage waveform includingsine waves and cosine waves.

The detection signals are input into controller 8 in an approximatelysaw-tooth waveform data. However, the number of gear teeth or rotationspeed differs between first detection head 22 and second detection head23, causing the waveform data to be phase-shifted due to differentfrequency cycle between first detection head 22 and second detectionhead 23.

Using the two different detection signals from first detection head 22and second detection head 23, and respective number of teeth, controller8 runs a predetermined calculation to output a detected rotation angleof rotor 21 or the steering shaft to the electronic circuit of thevehicle, thereby performing various controls in vehicle operation.

At this time, spring 28 is fixed between the bottom surface of cover 26and the top surface of rotor 21 in a slightly sagged condition, thusforming a biasing spring by which rotor 21 rotates in a conditioncontacting on first detection head 22 resiliently. Therefore, the gearclearance between gear 21A and spur gear 22A or so-called backlash iseliminated enabling the rotation angle detector to perform a highlyaccurate detection without any error.

First detection head 22 and second detection head 23 are disposedperpendicularly to rotor 21, and enlarging the diameters or increasingthe number of teeth can be realized relatively easily, which can performthe rotation angle detection in a still higher accuracy.

As described in the exemplary embodiment of the present invention, firstdetection head 22 and second detection head 23 are disposedperpendicularly to rotor 21. By allowing spur gear 22A formed outsidethe periphery of first detection head 22 to engage with gear 21A formedon the bottom of the periphery of rotor 21, first detection head 22 canbe provided with a simplified configuration with only one spur gear 22A.Furthermore, since magnetic sensors 5B and 6B, and controller 8 can beformed on a single circuit board 24, the rotation angle detector canperform the detection reliably and cheaply.

By contacting rotor 21 on first detection head 22 resiliently usingbiasing spring of spring 28, the clearance between gears of rotor 21 andfirst detection head 22 or so-called backlash can be eliminated,enabling the rotation angle detector to perform a highly accuratedetection without any error.

Moreover, another exemplary embodiment is shown in the partialperspective view in FIG. 2. Auxiliary detection head 30 with spur gear30A formed outside the periphery is provided further, which is allowedto engage with gear 21A formed on the bottom of the periphery of rotor21 and is provided with a detection section to detect rotation ofauxiliary detection head 30 itself. Controller 8 compares the rotationsbetween auxiliary detection head 30, and first detection head 22 andsecond detection head 23. If any difference between the detectionsignals is detected, for instance in a case of a gear out of mesh fromrotor 21 or an occurrence of breakage or crack in either gear of therotation angle detector, it can prevent erroneous detections of therotation angle.

The rotation angle detector of the present invention can detect therotation angle reliably with a simplified and low-cost configuration andis useful mainly to detect the rotation angle of steering shaft of avehicle.

1. A rotation angle detector comprising: a rotor to rotate in response to a steering shaft rotation; a first detection head to rotate in response to a rotation of the rotor; a second detection head to rotate in response to the rotation of the first detection head; a first detection section to detect the rotation of the first detection head; a second detection section to detect the rotation of the second detection head; and a controller to detect a rotation angle of the rotor according to detection signals output from the first detection section and the second detection section, wherein the first detection head and the second detection head are disposed perpendicularly to the rotor.
 2. The rotation angle detector of claim 1, wherein a gear is formed on a bottom of a periphery of the rotor, and a gear formed outside of a periphery of the first detection head is engaged with the gear formed on the bottom of the rotor.
 3. The rotation angle detector of claim 1 further comprising a biasing spring, wherein the biasing spring allows the rotor to contact the first detection head resiliently.
 4. The rotation angle detector of claim 2 further comprising a biasing spring, wherein the biasing spring allows the rotor to contact the first detection head resiliently. 